Embodiments of the present invention relate to wireless communication systems and, more particularly, to single-carrier frequency-domain multiple access (SC-FDMA) systems with multiple DFT-precoding stages.
An increasing data demand in cellular networks has resulted in the deployment of small cells providing Long Term Evolution (LTE) connectivity to a smaller number of users than the number of users typically served by a macro cell. This allows both providing larger transmission/reception resource opportunities to users as well as offloading the macro network. Technical challenges of the Radio Access Network (RAN) of small cells have been the focus of considerable standardization effort through 3GPP releases 10-12. It is a difficult technological challenge, especially for outdoor small cell deployment due to the non-conventional locations of small cell sites such as lamp posts, road signs, bus shelters, and traffic signals.
The LTE wireless access technology, also known as Evolved Universal Terrestrial Radio Access Network (E-UTRAN), was standardized by the 3GPP working groups. Orthogonal frequency-division multiple access (OFDMA) and SC-FDMA schemes were chosen for the downlink (DL) and uplink (UL) of E-UTRAN, respectively. User equipments (UEs) are time and frequency multiplexed on a physical uplink shared channel (PUSCH) and a physical uplink control channel (PUCCH), and time and frequency synchronization between UEs guarantees optimal intra-cell orthogonality. The LTE air-interface provides the best spectral-efficiency and cost trade-off of recent cellular networks standards, and as such, has been vastly adopted by operators as the unique 4G technology for the Radio Access Network (RAN), making it a robust and proven technology. As the tendency in the RAN topology is to increase the cell density by adding small cells in the vicinity of a legacy macro cells, the associated backhaul link density increases accordingly and the difference between RAN and backhaul wireless channels also decreases. There are several special issues associated with small cell sites, such as a requirement for high reliability with a packet error rate (PER) of 10−6, sparse spectrum availability, critical latency, cost, and relaxed peak-to-average power ratio (PAPR). Behavior of small cell sites also differs from RAN in that there is no handover, remote units do not connect and disconnect at the same rate as user equipment (UE) and the non-line-of-sight (NLOS) remote unit (RU) and small cell site is not mobile.
While preceding improvements in small cell topology have provided significant improvements in data throughput, the present inventors recognize that still further improvements are possible. Accordingly, the preferred embodiments described below are directed toward this as well as improving upon the prior art.